MOSCOW (Reuters) -- President Dmitry Medvedev has dismissed the head of Russia's powerful military intelligence service, the Kremlin said.

The Kremlin said Medvedev had signed a decree to dismiss Valentin Korabelnikov, a 63-year-old spymaster at the helm of the military intelligence service (GRU) since 1997. The Kremlin gave no reason for the dismissal.

Aleksandr Shlyakhturov was appointed as his replacement, it said.

Russia's GRU is the country's biggest spy agency, with agents all over the world. It is controlled by the military General Staff.